1. Ans Pardons (with input from Jean-Marc Cravero) CERN CNGS Horn Experience (issues since NBI2010) Ans Pardons, CERN 1 NBI2012

2. Outline Introduction –CNGS Horns –Memorable Moments –Electrical Properties –Power Convertor Circuit CNGS horns operation issues 2010-2012 –Exit Inductances –Thyristor –Capacitor Banks Summary 2 Ans Pardons, CERN

3. Introduction: CNGS horns 150/180kA, 0.3Hz avg. (20Hz inst.) Water-cooled Design lifetime: 20 10 6 double pulses CERN Gran Sasso 3 Ans Pardons, CERN

4. Introduction: CNGS horns Ans Pardons, CERN 4 Underground: 150/180kA 7.7kV, 9.4kA (horn) 6.3kV, 5.6kA(refl) Water cooling & Demineralisation (20m) High Voltage cables (1km, 12 per horn) On the surface HORN/REFLECTOR POWER CONVERTORS TRANSFORMERS X16(H) x32 (R)

5. Introduction: Memorable Moments 5 Ans Pardons, CERN Double pulses

6. Introduction: Memorable Moments 6 Ans Pardons, CERN 2006: water outlet leak –Badly designed brazed & machined ceramic assembly –All brazed ceramics in horns replaced 2007: broken stripline cable –Insufficiently restrained & brazing-weakened cables –Replaced with restrained & (more) rigid solution of Ag- plated copper plates

7. Introduction: Electrical Properties Ans Pardons, CERN 7

8. Converter Circuit Diagram Ans Pardons, CERN 8 1 st 2 nd

9. Ans Pardons, CERN 9 History –Recuperated from WANF, no documentation at the time –Found later from manu- facturer’s documentation: Under-dimensioned for CNGS –Replaced with new, correctly dimensioned inductances  all OK Failure details Mechanical fatigue  Insulating foil degradation  Short circuit at the exit of the power converters Exit Inductance Failure: mid 2011

10. 10 Thyristor Issues: Mid 2011 Thyristor firing board Inductance For pulse 1 - Pulse 2 Thyristor stack for pulse 1 – pulse 2 At each inductance failure –The output of the converter is in short-circuit, leading to the destruction of the thyristor stacks Additional observation –Sometimes pulse 1&2 fired at the same time due to the EM susceptibility of the thyristor firing board –Problem solved with filter added on the board and additional EM shielding

11. Capacitor Banks Issue: Early 2012 Ans Pardons, CERN 11 History –New capacitors installed in 2006, 24 capacitor cans per horn –Designed for 20 million pulses at 10kV Performance –During machine stop early 2012, measured capacitance value found to be at ˜50% (horn) and 90% (reflector) of nominal –At this moment, only 10 million pulses and max. 7kV  life time issue

12. Capacitor Banks Issue: Early 2012 Ans Pardons, CERN 12 Solution –For 1 st half of 2012: 7 spare cans (original design) were installed  horn up to 84%  ok until new –In June 2012: 24 new cans installed in the horn converter (new design from manufacturer) –No degradation observed since Reason for premature wear-??? –Unknown (awaiting tests results from manufacturer)

13. Summary 2006-2010: Many mechanical issues, lots of repair & re-design work done, many lessons learnt (and in parallel: enhancement of other systems) This seems to have paid off: no mechanical or cooling issues in 2010-2012 2010-2012: Electrical issues found and solved Lessons learnt: –Double check when recuperating existing equipment  Do look the gift horse in the mouth! –Capacitor banks have to be measured on a regular basis to detect life time issues (early). –EM compatibility is always a tricky issue when dealing with kA current pulses Ans Pardons, CERN 13